WO2007112861A1

WO2007112861A1 - Screw element

Info

Publication number: WO2007112861A1
Application number: PCT/EP2007/002482
Authority: WO
Inventors: Michael Behling; Ralf J. Dahl
Original assignee: Kraussmaffei Berstorff Gmbh
Priority date: 2006-03-28
Filing date: 2007-03-21
Publication date: 2007-10-11
Also published as: CA2644925A1; US20090016147A1; EP2001650B1; CN101400500B; RU2008142522A; CA2644925C; JP5130285B2; TW200800569A; JP2009531199A; DE102006014692B3; RU2442688C2; TWI432309B; CN101400500A; EP2001650A1

Abstract

A screw element, in particular a kneading element (1), to be used with a plasticating unit, having a screw shank with at least two kneading units, wherein the kneading units can be arranged on a common axis, for example the screw shank, and wherein the kneading units have a geometry, is designed with a view to particularly good plastication and reduced mechanical stress in such a way that the geometry of at least two successively arranged kneading units differs.

Description

description

screw element

The invention relates to a screw element according to the preamble of claim 1.

In the processing of plastics in a plasticizing unit, such as those in extruders or in injection molding machines, a variety of methods are used. One of these methods is compounding, i. the incorporation of fillers or reinforcing agents, incorporation of paints or pigments, blending of various materials, e.g. Plastics or elastomers, reactive processes or the like. All methods have in common that this is done by means of two- or multi-shaft extruder having in the same direction or in opposite directions rotating screws. Scissor energy is used to melt the plastic materials into the material by means of the screws. The screws have so-called screw elements, which are often designed to be multi-threaded.

A special screw element is the so-called kneading element, also called kneading block in the literature. Such a kneading block consists of spiral-shaped screw parts or a plurality of kneading units arranged one behind the other in the direction of the method and having a certain geometry. In the known kneading elements, the geometry of the kneading units, especially in terms of their width and their outside and inside diameters, is the same, and is determined by the size of the plasticizing unit, i. the plasticizing unit of the extruder or the injection molding machine selected.

The dissipation of the mechanical energy introduced via the drive via a gear and via the worm shaft is determined by, for example, the dependence of the enthalpy of the plastic to be processed on the type of worm assembly used. The type of screw assembly used is also called configuration. The configuration varies, for example, in the type and number of kneading blocks and the other screw elements. Notably, the main conversion of the energy depending on the geometry of the screw elements is achieved directly in front of and above the first or the first kneading elements. This major transformation of energy is through shear. In this case, primarily the speed of the screw and thus the (angular) speed of the kneading units, the gaps between the kneading unit and the extruder housing and in a twin-screw extruder the kneading units in the gusset area and the comb surface of the kneading elements are determining. From these quantities, the shear rate as well as the shear stress can be calculated accordingly. About the shear stress results in the melting of the material to be plasticized. During melting, the highest mechanical loads for the screw element and their shaft / hub connection result.

Such a kneading element is known from the registered documents of German Utility Model 82 32 585. The screw element shown there comprises individual kneading units, which can be plugged together to form a kneading element. The kneading units have the same geometry.

DE 100 50 295 A1 describes a multi-shaft extruder for the treatment and / or processing of an elastomer filled with filler with at least two shafts, which in the conveying direction comprise a filling zone, a mastifying zone and a dispersing zone. In this case, the masticating as well as the dispersing section may have kneading disks whose maximum diameter increases or decreases in the direction of production.

In the abstract of JP 2004202871 a kneading screw is described which has a kneading section between two conveying sections whose kneading disks have a continuously increasing diameter in the conveying direction.

DE 199 50 917 A1 deals with a twin-screw extruder with certain pebble elements, in which, with good dispersive mixing action, the lowest possible dissipative temperature increase occurs. Only in general is it stated in the introduction to the introduction that screw elements can have continuous pitch angles (twists) or else disks of variable width, whose pitch is infinite (no twisting) or arranged at an angular offset (so-called kneading blocks) can be provided.

The present invention is therefore based on the object of specifying a screw element of the type mentioned, in which a good plasticization of the material to be processed is made possible with reduced mechanical stress on the screw elements.

According to the invention the above object is achieved by a screw element with the features of claim 1.

Thereafter, the screw element in question is designed and refined such that the geometry of at least two successively arranged kneading units differs, wherein the width of the kneading units increases in the process direction

Thus, the width of at least two kneading units could be different. This would affect the shear gap to change the shear area. As in the case of a change in the diameter of the kneading unit, which will be discussed below, this could take place within one or more successive screw elements. The kneading units or screw parts do not have the same width throughout the width of the screw element. In addition, the kneading units or screw sections could not consistently have a same diameter. The screw elements could be independent of the number of elements in the screw. Thus, the disk land width variability could extend over several screw elements. The screw elements could thus be independent of length.

Overall, the width of the kneading units increases in the process direction. This would also increase the shear of the material to be plasticized in the process direction. The direction of the plasticizing unit, in which the material to be plasticized and / or plasticized is essentially transported, is thus defined as the method direction. However, the sequence of variability of the width of the kneading units does not have to increase steadily, but may be partially the same. Overall, it has been recognized that to obtain a good plasticization with reduced mechanical stress of the screw element can deviate from the known shape of the same geometry of the kneading units. If one chooses different geometries, namely different widths, in the kneading units, it is possible to control the initiation of the shear and the mechanical load and to optimize the respective method.

The use of the screw elements according to the invention is possible in a large number of plasticizing units and a wide variety of methods. The kneading elements according to the invention are conceivable in two- or multi-shaft, in the same direction or in opposite directions rotating plasticizing. It is also possible that the screw elements are designed to be single or multi-threaded, consist of spiral-shaped screw parts or integrally executed or loosely connected kneading units. The kneading units are selected depending on the size of the plasticizing unit and the respective process task. The inventive design of the screw element is therefore independent of the size of the machine and the diameter of the screw element. Furthermore, the screw elements are independent of the type of shaft / hub connection and the mobility of the screw element. The screw elements can furthermore be used in any type of material to be plasticized and are independent of the Da / D ratio and the direction of rotation of the screws.

In a particularly advantageous manner, the geometry of the kneading units is designed such that a continuous increase in the shear of the material to be plasticized can be achieved. This would have the particular advantage that the initiation of shear can not be massive and sudden, but sliding, for example, steadily increasing, can be configured. Mechanically, such an embodiment would be particularly advantageous, since the load of the element is also rather rising swell over a longer distance than locally brachial in a narrow limited area.

As already mentioned, the diameter of at least two kneading units could also be different. As a result, the shearing gap formed between the kneading unit and the extruder housing would be larger or smaller in the direction of the method. be stopped. In a preferred embodiment, the diameters of the individual kneading units or sections could increase in the process direction. The kneading units and kneading elements arranged one behind the other could have different diameters throughout.

However, the sequence of diameters does not necessarily increase steadily, but can also be partially the same or decrease. Depending on the process task, however, all possible variations of the diameter are conceivable. The diameter variability may extend over different screw elements.

With an increase in the diameter of the kneading units in the process direction, the mechanical stress of the element would be increasing swelling over a longer distance. The sequence of the variability of the diameter of the kneading units, however, need not increase steadily, but may be partially the same or decrease.

The variability of the geometry thus has a direct influence on the development of the shear rate and the shear stress in front of and in the screw element as well as on the development of the mechanical loading of the elements. Furthermore, the Da / Dj ratio of the kneading units may be constant or vary in the screw element according to the invention.

In an advantageous embodiment, the diameter and the width of at least two kneading units could be different. This would allow a particularly large variability of the shear gap. Such a configured screw element would also be particularly adaptable to a variety of process tasks.

In the context of a particularly good initiation of the shear and in terms of a balanced load on the shear element, both the diameter and the width of the kneading units in the process direction could increase.

There are now various possibilities to design and develop the teaching of the present in an advantageous manner. For this purpose, on the one hand to the claims subordinate to claim 1 and on the other hand to the following Er- Refinement of preferred embodiments of the screw element according to the invention with reference to the drawing. In connection with the explanation of the preferred embodiments of the screw element according to the invention with reference to the drawing, generally preferred embodiments and developments of the teaching are explained. In the drawing show the

1 is a schematic plan view of an embodiment of a screw element with variable diameter,

2 shows a schematic side view of the embodiment of a variable diameter screw element shown in FIG. 1, FIG.

Fig. 3 is a schematic plan view of an embodiment of a screw element according to the invention with variable width of the kneading unit and

Fig. 4 is a schematic side view of the embodiment shown in Fig. 3 of a screw element according to the invention with variable width of the kneading unit.

In the embodiments shown, the screw element is a kneading element 1, which is used for use in a plasticizing unit, not shown, with a worm shaft, also not shown.

The kneading element 1 is composed of kneading units 2, which are firmly connected to each other in this embodiment. The kneading units 2 can be arranged on a common axis. For this purpose, the kneading units 2 have a toothing, which can be brought into engagement with a toothing on the worm shaft and thus the kneading element is fixed substantially rotationally fixed on the worm shaft. The kneading units 2 have a geometry which is determined by two diameters Di and D _a , ie the diameters D ₁ and D ₂ , D ₃ or D ₄ .

In this case, the geometry of two kneading units 2 arranged one after the other differs. In the case of the kneading element shown in FIG. 1, it is the case that the external diameter of the kneading element 2 shown in FIG. knife D ₃ increases in the process direction. This means that the kneading unit 2 with the smallest diameter Di in this embodiment is arranged closest to the feeding zone and the kneading disk 2 with the outside diameter D ₄ is arranged furthest in the direction of the discharge zone. In the exemplary embodiment shown here, therefore, D _{4 is} greater than D ₃ and D _{3 is} greater than D ₂ . Di is again smaller than D ₂ , ie Di <D ₂ <D ₃ <D ₄ . The inner diameter Di of the kneading element 1 remains constant. It is conceivable in any configuration that the inner diameter Dj varies according to or other than the outer diameter D _a .

FIG. 2 shows the kneading element 1 shown in FIG. 1 in a schematic side view. The kneading element 1 of this embodiment has an overall width B. The kneading units 2 in turn have a width b.

FIG. 3 shows a kneading element according to the invention with a variable web width, ie that the kneading units 2 have different widths b. The diameter ratio DJD ₁ is constant in this embodiment. It should also be noted that the outer diameter D _{3 is} also constant. The width b of the kneading units 2 increases in the process direction. Thus, the shear of the material over the width B of the kneading element 1 is increased. In this concrete embodiment, the width bi of the kneading unit 2, which is arranged closest to the feeding zone in this kneading element 1, is smaller than the width b ₂ . The width b ₂ is again smaller than the width b ₃ . The width b _{4 of} the next kneading unit 2 is again greater than the width b _{3 of} the previous kneading unit 2. Furthermore, the width bs of the kneading unit 2, which is located farthest in the direction of the discharge zone with respect to this kneading element 2, is greater than the width b ₄ . ie bi <b ₂ <b ₃ <b ₄ .

For further details, refer to the general description to avoid repetition.

Finally, it should be expressly understood that the embodiments described above are only for the purpose of discussion of the claimed teaching, but not limit these to these embodiments. LIST OF REFERENCE NUMBERS

1 kneading element

2 kneading unit

D _a> Di, D ₂ , D ₃ , D ₄ outer diameter

Di inside diameter kneading unit b width of kneading unit

B Width of the kneading element

Claims

claims

1. screw element, in particular kneading element (1), for use in a plasticizing unit with a worm shaft, with at least two kneading units (2), wherein

the kneading units (2) can be arranged on a common axis, for example the worm shaft,

- The kneading units (2) have a geometry and

- The geometry of at least two successively arranged kneading units (2) differs, characterized in that the width (b) of the kneading units (2) increases in the process direction.

2. Screw element according to claim 1, characterized in that the diameter (Di, D ₂ , D ₃ , D ₄ ) of at least two kneading units (2) is different.

3. screw element according to claim 2, characterized in that the diameter (Di, D ₂ , D ₃ , D ₄ ) of the kneading units (2) increases in the process direction.